1. Field of the Invention
The present invention relates to a magnetic head having a magnetoresistive film.
2. Description of the Related Art
As a well known method for reading a signal that has been recorded on a magnetic recording medium, a inductive-type read head is relatively moved against the recording medium and a voltage induced in the coil by the electromagnetic induction is detected. In addition, a magnetoresistive (MR) head using the phenomenon of which the electric resistance of a ferromagnetic substance varies corresponding to the intensity of an external magnetic field is also known as a high sensitivity head that detects a signal magnetic field of the recording medium (see IEEE MAG-7, 150, 1971). In recent years, as small-sized large-capacity magnetic recording units are required and the relative speed between the read head and the recording medium becomes small, the MR head that can output a large output signal regardless of the relative speed becomes important.
Conventionally, in the magnetoresistive head, an MR element portion whose resistance varies corresponding to the external magnetic field is composed of an alloy of Ni (80 atomic %) and Fe (20 atomic %) (this alloy is referred to as a permalloy) is used. The MR change ratio of the permalloy that has a good soft magnetic characteristic is at most around 3%. Thus, a material that has a higher MR change characteristic has been desired. In recent years, laminate films composed of a ferromagnetic metal layer and a non-magnetic metal layer such as Fe/Cr and Co/Cu that have giant MR change ratios (for example, 100% or more) have been reported (see Phys. Rev. Lett., Vol. 61, 2472, 1988 and Phys. Rev. Lett., Vol. 64, 2304, 1990). In addition, it has been reported that when the thickness of a non-magnetic layer is varied, the MR change ratio periodically varies because the magnetic coupling between an adjacent ferromagnetic metal layers changes periodically. In the case of the antiferromagnetic coupling state, the electric resistance of the laminate film is high because the direction of magnetization of an adjacent magnetic layers is opposite. In contrast in the case of the ferromagnetic coupling state, the electric resistance of the laminate is low because the direction of magnetization of an adjacent magnetic layers is the same. Thus, the magnetic layers are antiferromagnetically coupled when the external magnetic field is absent. Thereafter, an external magnetic field that exceeds the saturated magnetic field is applied to the laminate film. Thus, the laminate film is ferromagnetically coupled. Consequently, the magnetoresistance of the laminate film can be changed.
However, in the antiferromagnetic coupling state, since the coupling force is large, the saturated magnetic field becomes large. To solve such a problem, several methods to realize the antiparallel state of magnetization, without using the large antiferromagnetic coupling state, have been reported.
As a first example, using adjacent magnetic layers having different coercive forces, antiparallel state of magnetization is realized (see The Magnetics Society of Japan, Journal, Vol. 15, No. 5, 813, 1991). As a second example, an exchange bias of an antiferromagnetic layer is applied to one of two ferromagnetic layers with a non-magnetic interlayer so as to pin the magnetization of the layer. The other ferromagnetic layer (we call the rotatable magnetization layer) is reversely magnetized by the external magnetic field. Thus, antiparallel magnetization state is realized. Consequently, a large MR change is accomplished (see Phys. Rev. B., Vol. 45806, 1992 and J. Appl. Phys., Vol. 69, 4774, 1991). In particular, an element of which the direction of magnetization of the pinned magnetization layer is along perpendicular to an easy axis of magnetization of the rotatable magnetization layer (the soft magnetic layer whose magnetization rotates corresponding to the signal field) has been proposed on a spin valve type magnetic layer. In this element, it is not necessary to bias the operating point like a conventional MR element with a single magnetic layer, if the perpendicular magnetization alignment state is realized at a signal field=0 (as disclosed in Japanese Patent Laid-Open Publication No. 4-358310).
As described above, several MR elements using the theory of spin dependent scattering have been proposed. However, when these MR elements are formed in rectangular patterns for applying to magnetic heads, the achievement of perpendicular magnetization alignment state between the pinned magnetic layer and the rotatable magnetization layer is disturbed because of the magnetostatic coupling between the two magnetic layers. Thus, the operating point is largely shifted. Consequently, since the rotatable magnetization layer does not respond sharply to the signal magnetic field, a good linear characteristic to the signal magnetic field cannot be obtained, resulting in an output distortion.